Noise may be present not only due to a headset failure, but also due to a state of the Bluetooth wireless communication or the smartphone.
Try the following:
- Update the headset’s software to its latest version.
- Keep any obstacles, including people, out of the Bluetooth communication path between the headset and the smartphone.
- Devices that use a 2.4 GHz frequency band, such as a microwave oven, a Bluetooth device, and a digital cordless device, may disturb the wireless communication. Move those devices away or turn them off.
- Change the Bluetooth sound quality setting of your smartphone from "High quality" to an option, such as "Standard" or "Priority on communication". For details, refer to the user manual for the smartphone you are using.
Additionally, if you are using some device that runs on Android 8.0 or later, change the Music Center's wireless playback quality to [Prioritize Connection (Auto)]. You can change the wireless playback quality from  on the right side of the Music Center screen - [Music Center Settings] - [Bluetooth Output Settings].
- Change the sound quality mode of the "Sony | Headphones Connect" app or the headset to the one with "Priority on connection".
- Restart the smartphone.
- When you are listening to music with a smartphone, exit the unused apps running on the smartphone.
- When listening to music from the Bluetooth-connected computer, quit any unnecessary apps. Restarting the computer may provide improvement.
- If multiple devices concurrently access a single Wi-Fi access point for playing music from music services or songs stored on a computer, the network communication speed may slow down. Minimize network use, such as internet access for devices other than the smartphone that is playing music.
- Delete the device information of the headset from the smartphone, and then pair the headset with the smartphone again.